8. Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Marketable securities	$ 494,080	$ 811,506
Restricted marketable securities	253,236	223,785
Foreign debt [Member]
Assets:
Marketable securities	261,955	387,820
Foreign government obligations [Member]
Assets:
Marketable securities	0	22,011
U.S debt [Member]
Assets:
Marketable securities	48,697	66,134
Time deposits [Member]
Assets:
Marketable securities	183,428	335,541
Fair Value, Recurring [Member]
Assets:
Restricted marketable securities	253,236	223,785
Derivative assets	1,708	1,338
Total assets	749,416	1,043,951
Liabilities:
Derivative liabilities	9,786	10,021
Fair Value, Recurring [Member] \| Foreign debt [Member]
Assets:
Marketable securities	261,955	387,820
Fair Value, Recurring [Member] \| Foreign government obligations [Member]
Assets:
Marketable securities		22,011
Fair Value, Recurring [Member] \| U.S debt [Member]
Assets:
Marketable securities	48,697	66,134
Fair Value, Recurring [Member] \| Time deposits [Member]
Assets:
Marketable securities	183,428	335,541
Fair Value, Recurring [Member] \| Money Market Funds [Member]
Assets:
Cash equivalents	392	7,322
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets:
Restricted marketable securities	0	0
Derivative assets	0	0
Total assets	183,820	342,863
Liabilities:
Derivative liabilities	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Foreign debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Foreign government obligations [Member]
Assets:
Marketable securities		0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| U.S debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Time deposits [Member]
Assets:
Marketable securities	183,428	335,541
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Money Market Funds [Member]
Assets:
Cash equivalents	392	7,322
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets:
Restricted marketable securities	253,236	223,785
Derivative assets	1,708	1,338
Total assets	565,596	701,088
Liabilities:
Derivative liabilities	9,786	10,021
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign debt [Member]
Assets:
Marketable securities	261,955	387,820
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign government obligations [Member]
Assets:
Marketable securities		22,011
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| U.S debt [Member]
Assets:
Marketable securities	48,697	66,134
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Time deposits [Member]
Assets:
Marketable securities	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Money Market Funds [Member]
Assets:
Cash equivalents	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Assets:
Restricted marketable securities	0	0
Derivative assets	0	0
Total assets	0	0
Liabilities:
Derivative liabilities	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Foreign debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Foreign government obligations [Member]
Assets:
Marketable securities		0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| U.S debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Time deposits [Member]
Assets:
Marketable securities	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Money Market Funds [Member]
Assets:
Cash equivalents	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

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